Space Environmentally Stable Polyimides and Copolyimides Derived from Bis(3-Aminophenyl)-3,5-Di(Trifluoromethyl)Phenylphosphine Oxide

Abstract

Polyimides with a unique combination of properties including low colour in thin films, atomic oxygen (AO) resistance, ultra-violet (UV) radiation resistance, solubility in organic solvents in the imide form, high glass transition (T_g ) temperatures, and high thermal stability have been prepared and characterized. Polyimides were prepared by reacting a novel aromatic diamine, bis(3-aminophenyl)-3, 5-di(trifluoromethyl)phenylphosphine oxide, with various aromatic dianhydrides in a polar aprotic solvent. Copolymers were prepared by the addition of a second diamine. The solubility of the polymers in the imide form as well as the colour density of thin films was dependent upon the chemical structure of the dianhydride and the additional diamine. Thin films (25–50 μm thick) prepared by solution casting of amide acid or imide solutions exhibited very low colour and high optical transparency as determined by UV/visible spectroscopy. The polymers exhibited T_g values greater than 200 °C depending upon the structure of the dianhydride and temperatures of 5% weight loss ∼500 °C in air as determined by dynamic thermogravimetric analysis (TGA). Thin films coated with silver/inconel were exposed to a high fluence of AO and 1000 equivalent solar hours of UV radiation. The effects of these exposures on optical properties were minor. These space environmentally durable polymers are potentially useful in a variety of applications on spacecraft such as thin film membranes on antennae, second surface mirrors, thermal/optical coatings and multi-layer thermal insulation (MLI) blanket materials. The chemistry, physical and mechanical properties of the polymers as well as their responses to AO and UV exposure will be discussed.